The present invention relates to head positioning control systems in data storage systems and in particular to servo sector formats and associated control systems for positioning a transducer head over a desired data track.
In data storage devices, user data is typically stored on concentric tracks of data located on the surface of the storage media. In addition to the data tracks, position data is also provided on the storage media. The position data can include servo marks that, when read, generally indicate position coordinates (e.g. X, Y coordinates, track number, or sector number) of a transducer head relative to the storage media surface, and in particular to a desired data track over which the transducer head should be positioned. Such devices also include a servo system that positions the transducer head over a selected track based on feedback of the position data. The servo system may have a “seek mode” that moves the transducer from one track to another track based on reading the servo marks. The servo system also may have a “tracking mode” in which the transducer is precisely aligned with a selected track based on a reading of the servo marks.
A particular sub-set of servo marks include permanent servo marks that are created through lithographic processes on the storage device at the time of manufacture. During operational use of the data storage device, the transducer reads the servo marks but there is typically no need to erase and rewrite servo data during operation. The position of permanent servo marks on the media for a magnetic data storage device is therefore stable and does not change significantly during the operational life of the data storage device.
Various lithographic processes may be employed to create the permanent servo marks on the storage device, such as low-energy ion implantation, defect mapping, and imprint annealing. However, each of these methods requires a lithographic master pattern to generate the relevant servo marks. In conventional servo sector formatting, the size of the servo marks are equal to the size or pitch of the data tracks they help to identify. As track widths continue to decrease to provide higher density data storage, the costs associated with lithographically producing servo marks of equal size increases.
Therefore, a need has been shown to exist for servo sector formats having large lithographic tolerances that can still be used to position a transducer over a desired track.